The adaptation of a transmission scheme for a MIMO system may be formulated as a problem of throughput maximization with a given outage probability. Constraints on computational complexity make the problem closer to a real implementation.
A number of systems have been proposed for adapting transmission over a MIMO channel, but only a few such systems address the issue of MIMO scheme selection, while others cover power adaptation; see, for example, Z. Zhou, B. Vucetic, “MIMO Systems with Adaptive Modulation”, IEEE, proc. VTC04-Spring, and K. S. Kim, Y. H. Kim, J. Y. Ahn, “An Adaptive MIMO Transmission Technique for LDPC Coded OFDM Cellular Systems”, IEEE, proc. VTC04-Spring.
In “Adaptive transmission method in MIMO systems”, RCS2003-310, Y. Murakami, K. Kobayashi, M. Orihashi, and T. Matsuoka, of Matsushita Electric Industrial Co. Ltd., propose an adaptive MIMO system wherein a parallel stream approach is used for channels with a high signal-to-noise ratio (SNR), while an Alamouti approach is adopted for lower SNR. However, this adaptation is not only difficult to extend to more than two transmit antennas, due to the non-existence of rate-one orthogonal designs, but moreover does not account for the spatial properties of the channel.
In “Adaptive rate MIMO system using space-time block mapping”, IEEE 2003, K. J. Hwang, S. Lee, and K. H. Chang introduce a promising approach wherein the spatial multiplexing rate is adaptively modified based on channel features, such as SNR and correlation. This system, however, has not been fully developed.
Alternatively, some prior art characterizes a MIMO channel in view of adaptive transmission. For example, in “Characterization of MIMO channels for spatial multiplexing systems”, IEEE 2001, R. W. Heath Jr., A. Paulraj, proposes to use the Demmel condition number to assess the suitability of a channel to spatial multiplexing. Additionally, in “Measurement of Demmel condition number for 2×2 MIMO-OFDM broadband channels”, proceeding of VTC04-Spring, IEEE 2004, N. Kita, W. Yamada, A. Sato, D. Mori, and S. Uwano show the distribution of the Demmel condition number in real channels. However, based on simulations, adaptation based on the Demmel condition number does not perform as well as desired for some applications.
Accordingly, a continuing search has been directed to the development of a system and method for adapting transmission parameters in a multicarrier communication system having multiple transmit antennas and/or multiple receive antennas.